Dynamics of maculo-ocular reflexes in the frog

Abstract

Compensatory torsional and vertical eye movements were recorded in the frog during sinusoidal linear acceleration along the longitudinal and transverse body axes, respectively. Stimulus frequencies ranged between 0.1 and 1.0 Hz and peak accelerations from 0.01 g to 0.1 g corresponding to body tilts ranging from 0.57 to 5.7°. In addition, static compensatory eye movements were studied during fore-and-aft and lateral body tilt over ranges of± 10°. The evoked eye movements were generally quite small (± 0.5°). Dynamic gain (rotation of the eye/apparent rotation of gravity direction) was 0.10–0.20 at 0.1 Hz and decreased to about 0.05 at 1.0 Hz. The gain of vertical eye movements was somewhat higher than that of torsional eye movements. Phase lag relative to peak accelerations increased from about 10° to about 45° over the same frequency range. Static compensatory eye movements evoked by nose-up and ipsilateral side-up tilt were larger in amplitude than those evoked by nose-down and ipsilateral side-down tilt. Static gain (rotation of the eye/tilt of the whole body) was about 0.10 for vertical and about 0.06 for torsional eye movements. No consistent eye movements could be evoked by vertical sinusoidal accelerations (maximal modulation amplitudes± 0.025g). The results indicate that, as in other vertebrates, maculo-ocular reflexes contribute to gaze stabilization in the frog mainly during low frequency and static head and body tilts.